Note: I've moved this post from the truck forum

This is my first post and I appreciate any and all feedback.

Vehicle:
I have a 1997 (I bought new in 1997) Nissan pickup with 197 K miles on it. It has a KA24 engine and a 5 speed manual transmission.
The engine is completely original except for the valve job I had a shop do 2 years ago and the new timing chain / oil pump / water pump I had a shop do 6 months ago.

Symptoms:
Prior to the timing chain replacement the idle was little rough but I had assumed that new plugs and wires would resolve the issue. So I don't believe the timing chain effort had any root cause. Even after some fresh ignition parts the rough idle gradually got worse in daily driving to the point that I had to keep my foot on the gas pedal at stops to prevent the engine from stalling. At idle the engine would cycle between 500 and 800 RPM. While driving at higher engine RPM the engine runs great. There are no engine fault codes showing.

Research thus far:
I've done plenty of online research thus far and this appears to be a fairly common symptom but the root causes seem to vary quite a bit.

Background:
I did a smoke test and found some leakage around the base of the fuel rail where the number one injector sits in the intake manifold. I'm currently waiting for some new fuel rail cushions (I actually had to order those through a dealer) and injector seals to reinstall everything. While I'm guessing the vacuum leak certainly needed fixing it didn't seem so significant that it would been the only root cause. I won't know until I get it back together.

Online research has also pointed toward the IACV, MAB, FPR, and injectors.

Has anyone else on the forum had similar issues with the KA24 engine?
I will also post my results as the project develops.

Thanks

Like so many problems folks have, if there was some data showing what was good and what was not, better suggestions could be made here. It may not have anything to do with it, but there was a bad ground splice on these (and other trucks) which created a poor signal from the TPS, ETS and TPS. It is in a black wire, in the main harness near #4 injector. The original just used a brass crimp connector, we soldered it up.
If you have a data stream, you can watch the values of these components while wiggling the harness and watching if the values change.

Hey ezb, thanks for that input!

I haven't read anything about this splice before. This gives me one more potential for solving this issue.

My diagnostic approach / equipment set is most definitely low tech / low budget. My vacuum leak / smoke test tools consisted of a roll of masking tape, a length of vacuum hose, a hose barb, and a cheap cigar......low tech but found a leak around the base of the #1 injector.

I just received the new fuel rail cushions and injector o-rings today. I did find one other post in the forum from 2011 indicating a similar symptom from a rotted fuel rail cushion / injector seal leak.

I intend to re-install the fuel rail tomorrow.

I'll post my results.....thanks again

Ok so here's the progress so far.

I ran a smoke test and found a leak coming from under the #1 injector cushion.

I removed the fuel rail and found some rough machining chatter marks in the manifold well where the injector cushion sits.

I cleaned out all 4 wells and replaced the fuel rail cushions as well as the #1 injector o-rings.
I included a thin coat of black RTV on the bottom of the #1 cushion to fill the rough machining marks.

I ran another smoke test to confirm the leak was resolved.

As suspected resolving this leak was not the only issue however it did make a dramatic difference.

Now the engine will idle (after some adjustment of the idle screw) however it does migrate about 150 RPM's after its warmed up. I pulled the plug on the MAF and it made no difference (likely not the cause). I unplugged the IACV and the RPM migration decreased to about half. I unplugged the TPS and the engine tried to die.

Even though the truck is very driveable now I've still got more investigation to do and am focusing on the IACV, the TPS, and possibly the fuel delivery system. After looking over the throttle body configuration I'm probably going to remove the entire throttle body to replace the IACV....there's really not much working room.

That's what I've had time for lately. I'll post some pics If I can get some advice on how to do that.

This is actually my first fuel injected vehicle so it's been quite a learning experience.

A couple of things I've learned:
- high pressure fuel injection hose is $ 6.50 per foot
- every module, regulator, or sensor involved is $ 75 - $ 115.

My advice at this point is look for possible vacuum leaks first....